nUI6 does not have a '/nui' command -- I haven't decided if I'll be adding one or not. It's actually designed to use the WoW AddOns interface. If you try '/mfwm' (and click the "addons" tab since there's current a bug in Blizz's code for the addon panels) you'll get a glimps at what nUI6's configuration options will look like. Eventually there will be a screen for all of the nUI6 options there, too.
As for showing the buffs on the HUD... they are not there in the alpha code, either. The nUI6 alpha is tracking all of the auras and using them for the action bars, but it is not yet displaying them, which is why the default Blizz auras are still shown in the upper right corner of the screen.
What people don't get is that I am, ultimately, an artist at heart. My brush has two colors, 1 and 0, and my canvas is made of silicon.